Cresylic acid is an important commercial product widely used in the manufacture of chemical, agrichemical, pharmaceutical and industrial intermediate products. The lowest molecular weight member of the cresylic acid family, phenol, is produced synthetically in very large quantities. The three cresols also are produced synthetically, but in much smaller quantities. The dimethyl phenols (xylenols) and other alkylated phenols are not commercially synthesized to any appreciable extent with the exception of 2-, 6-xylenol. Therefore, recovery from natural sources such as partially refined petroleum and coal via coking, gasification, and liquefaction provides the majority of cresylic acid isomers used in industry today. Cresylic acids recovered from these sources are heavily contaminated with aromatic organic compounds including hydrocarbons as well as hetero-atoms such as nitrogen, sulfur and oxygen. Methoxy substituted phenols comprise a particularly troublesome group derived from some low grade coals such as brown coal or lignite. Guaiacol (ortho-methoxy phenol) boils near the boiling points of meta- and para-cresol and methyl guaiacols (methoxy cresols) boil in the range of the xylenols. Therefore, the guaiacol cannot be separated from the cresylic acid fractions by conventional distillation. To be useful, the various isomers of cresylic acid must be separated from the other impurities and often from each other, and therein lies the problem because, heretofore there has been no simple process for physically separating guaiacols from cresylic acid. Therefore, the guaiacol must be destroyed in the presence of the cresylic acid. This however, presents a problem of cresylic acid yield loss. The crude cresylic acid mixture obtained from lignite contains larger amounts of guaiacol than the mixture obtained from coal, up to almost 4% by weight, sometimes even more. Heretofore, such destruction has been accomplished only with difficulty and the resultant loss of cresylic acid yield to byproducts, most of them unwanted heavies and coke.
Considerable academic research has been reported relating to removal of methoxy compounds or the demethylation of phenols. This work is reported in articles, such as Lawson, J. and M. Klein, Influence of Water on Guaiacol Pyrolysis, Ind. Eng. Chem. Fundam., 24:203, 1985; Ceylan, R. and J. Bredenberg, "Hydrogenolysis and Hydrocracking of the Carbon-Oxygen Bond. 2. Thermal Cleavage of the Carbon-Oxygen Bond in Guaiacol," Fuel, 61:377, 1982; and Vouri, A. and J. Bredenberg, "Hydrogenolysis and Hydrocracking of the Carbon-Oxygen Bond. 4. Thermal and Catalytic Hydrogenolysis of 4-Propylguaiacol," Holzforschung, 38:133, 1984 relating to pyrolysis of guaiacol. Another dealkylation process by reacting acetic acid in the presence of an alumina-silica catalyst in the liquid phase is described in U.S. Pat. No. 2,697,732. The patent literature describes dealkylation processes and processes for the rearrangement of alkyl phenyl ethers to alkylated phenols. For example, a process is described in U.S. Pat. No. 4,381,413 for the preparation of cresylic acid using an alumina catalyst, calcined to create gamma alumina. This process requires temperature ranges of about 225.degree. C. to about 295.degree. C. in the presence of an effective amount of water to produce mixtures of ortho-methylated phenolic products such as o-cresol and 2-, 6-xylenol in high selectivity. Although temperatures at ranges above 325.degree. C. were discussed, they were not considered suitable for the desired selectivity of products. Even within the suggested optimum temperature ranges of this prior process, guaiacol removal was incomplete. A rearrangement process in presence of alumina is described in U.S. Pat. No. 4,447,657. None of the prior art processes for catalytic removal of guaiacol have been applied to purification of naturally occurring cresylic acid crude mixture.